Printing apparatus of the general type with which the present invention is concerned are known. They operate with a supply of tape arranged to receive an image and a means for transferring the image onto the tape. In one known device, there is a tape holding case which holds a supply of image receiving tape and a supply of an image transfer ribbon, the image receiving tape and the transfer ribbon being passed in overlap through a printing zone of the printing device. At the print zone, a thermal print head cooperates with a platen to transfer an image from the transfer ribbon to the tape. A printing device operating with a tape holding case of this type is described for example in EP-A-0267890 (Varitronics, Inc.). Other printing devices have been made in which letters are transferred to an image receiving tape by a dry lettering or dry film impression process. In all of these printing devices, the construction of the image receiving tape is substantially the same. That is, it comprises an upper layer for receiving an image which is secured to a releasable backing layer by a layer of adhesive.
The upper layer can either receive an image on its top surface, its lower surface being secured to the releaseable backing layer by a layer of adhesive or alternatively the upper layer can be transparent and can receive an image on one of its faces printed as a mirror image so that it is viewed the correct way round through the other surface of the tape. In this case, a double sided adhesive layer can be secured to the upper layer, this double sided adhesive layer having a releaseable backing layer. This latter arrangement is described for example in EP-A-0322918 (Brother Kogyo Kabushiki Kaisha).
With such printing devices, it is important to be able to determine when the tape holding case used with the device has exhausted its supply of image receiving tape so that a new tape holding case can be inserted into the device. If the printing device is run with no image receiving tape there is a danger that the print head or platen will be damaged by overheating. Damage to the platen can also result if an image is transferred to it by the print head operating with no image receiving tape.
Furthermore, it is desirable for printing apparatus of this type to be able to operate with image receiving tapes of different widths. For this, the apparatus should include a way of identifying the width of tape within the tape holding case automatically so that the user does not have to concern himself with setting the apparatus for different tape widths. There is a danger if the user is called upon to set the tape width that the tape width will be incorrectly set.
The present invention seeks to provide a printing apparatus in which these problems are both overcome.
According to the present invention there is provided a printing device comprising a zone for receiving tape for printing so that said tape passes along a predetermined path in the printing device; an optical sensing arrangement comprising first and second optical sensing assemblies each comprising a light emitter and a light receiver arranged to receive light emitted from the light emitter, the optical sensing arrangement being located so that when there is no tape in said predetermined path the light receivers of the first and second assemblies receive light from their respective light emitters and when there is tape present in the predetermined path it obstructs light from at least one of said light emitters so preventing it from reaching its light receiver; and a controller for receiving signals from said light receivers and for controlling operation of the printing device in response to said signals.
The tape for printing is conveniently housed in a tape holding case. Tape holding cases for use with the printing device can be supplied holding tapes of respective differing widths. The tape holding cases have similar external dimensions for reception by said zone but are arranged to accommodate internally tapes of respective differing widths. In one embodiment of the present invention a tape holding case is provided with a tape guide arrangement comprising a plurality of sets of tape guides, each set fitting a particular tape width. Thus, only one type of tape holding case needs to be manufactured and can accommodate reels of tape of different widths as desired. The sets of guides are located to guide the tape in cooperation with the optical sensing assemblies. Where two tape holding cases are arranged to supply tape of different widths along said predetermined path with a common centre line the optical sensing arrangement can be such that the first optical sensing assembly is located below the second. With this arrangement, with a tape holding case holding a narrow tape it will obstruct light only in the second optical sensing assembly and not in the first. With a wide tape, however, both of the optical sensing assemblies will be affected. The controller thus receives signals informing it either that there is no tape (where neither of the light emitters is obstructed), or that there is narrow tape present (where only the second of the light emitters is obstructed) or that there is wide tape present (where both of the light emitters are obstructed).
More than two widths of tape can be taken into account by providing further optical sensing assemblies located suitably. In one particular arrangement, a tape holding case can be arranged to accommodate tape narrower than the narrow width tape already mentioned. Where this tape is centered about the centre line the optical sensing arrangement requires a third optical sensing assembly located above the second assembly so that only the third optical assembly is affected by the tape when present. In another arrangement, the narrower tape is located in a tape holding case so that its lower edge corresponds to the lower edge of the widest tape so that it obstructs only the first light emitter and not the second light emitter. Thus, a different combination of signals is then supplied to the controller to indicate that there is this narrow tape, namely that only the first light emitter is obstructed.
The invention also contemplates the combination of a printing device and a cooperable tape holding case. A tape holding case can be provided with a housing which accommodates the tape and which has an aperture for receiving the optical sensing arrangement.
Typical tape widths are 19 mm, 12 mm and 6 mm although it will readily be appreciated that different tape widths can be used with the present invention.
It will be appreciated that in practice tape holding cases will be manufactured holding a single reel of tape of a predetermined width. When this is inserted into the device the device is immediately informed through the controller of the width of tape which is present and can thus set itself to appropriate label composition parameters. Thus, a user is not required to input into the machine what tape width is being used.
Moreover, when the tape in a tape holding case runs out the device will be advised through the controller and operation will be inhibited to prevent damage to the print head and platen.